1. Field of the Invention
This invention relates to a belt clutch control apparatus and, more particularly, to such apparatus having an improved linkage mechanism specially adapted for use on the cutting deck of a riding lawn mower.
2. Description of the Prior Art
Belt driven systems typically comprise a driving pulley, one or more driven pulleys, a continuous belt interconnecting the driving and driven pulleys, and an idler pulley. Selective movement of the idler pulley into or out of close engaging contact with the belt serves to tighten or loosen the belt, respectively, thereby engaging or disengaging the driving pulley with the driven pulley(s) as desired. Such belt driven systems are commonly used on riding lawn mowers to allow selective engagement of the cutting blades, which are typically connected to the driven pulley(s).
Belt driven systems typically include a belt clutch control apparatus for allowing the user to move the idler pulley between the engaged and disengaged positions, as desired, by selectively moving a control handle between its respective on and off positions. Such control apparatus customarily comprise an overcenter linkage system, which includes at least one connecting link moveable from an undercenter position to an overcenter position during movement of the control handle to its on position. Additional linkage members translate movement of the connecting link to a high-tension spring, which pulls the idler pulley into engagement with the belt and maintains adequate tension on the belt to prevent slippage. The high-tension spring also serves to hold the connecting link firmly in its overcenter position to prevent inadvertent disengagement of the system.
By design, an overcenter linkage system requires that at least a portion of the total control handle movement be devoted to locking the link in its overcenter position, even after the idler pulley has moved into full engagement with the belt. This extra degree of control handle movement is effectively wasted, since its only purpose is to move the connecting link through the center position to the overcenter position (or, to the undercenter position, when disengaging the system). This "wasted movement" results in less motion being utilized to stretch the idler pulley spring, necessitating the use of a stiffer spring (i.e., a higher spring rate) to develop the load required to adequately tighten the belt.
To reduce the frequency of adjustment, the spring must be overstretched to allow for a certain degree of relaxation which occurs as the belt system wears. With a stiff spring as required for conventional overcenter linkages, the spring load becomes unacceptably high when overstretched. The high degree of force required to move the control handle in a conventional overcenter linkage system is a problem well known to those skilled in the art.
The linkage system in a conventional belt clutch control apparatus on a riding mower typically includes a bellcrank pivotally mounted to either the underside of the frame or the top of the cutting deck. A bellcrank is commonly used to interconnect the connecting link and the idler pulley spring, with each being secured to an opposite end thereof. In order to avoid inadvertent stretching of the spring when the cutting deck is in its lowest position, and consequential engagement of the cutting blades, the spring must be long and slidably secured to one end of the bellcrank, so the point of attachment between the spring and the bellcrank may vary upon raising and lowering the deck. This variation increases the amount of wasted movement in the system when the deck is raised, and increases spring tension when the deck is lowered.
A number of problems have been recognized relating to the use of overcenter linkages in belt clutch control mechanisms, particularly in the context of a riding lawn mower. Due primarily to the generally high spring rate of the idler pulley spring in conventional systems, a considerable amount of force is necessary to move the connecting link to its overcenter position. The moment created by the spring about the control shaft may be extremely high, particularly just prior to entering the region of wasted movement described above. The idler pulley normally contacts the belt relatively early in the movement of the control handle, so that the spring is actively resisting the additional movement required to move the handle to the overcenter position. Accordingly, overcenter linkages are frequently difficult for some users to operate.
As explained above, conventional overcenter linkage systems require the use of a relatively stiff spring which is typically overstretched to allow for some relaxation as the belt wears. This naturally places the belt under greater tension than necessary, resulting in increased wear of the belt and pulleys as well as the spring itself, thereby increasing the maintenance needs of these components. Frequent adjustment and/or replacement of both the spring and belt is a particular problem with some riding mower linkage systems.
Once the connecting link has passed the center position during movement of the connecting link to the engaged position, the spring pulls the linkage firmly to the overcenter position. Similarly, during movement of the connecting link to its disengaged position, the spring pulls the linkage firmly, and rapidly, to its disengaged position. Such sudden movement of the linkage, and the resulting movement of the control handle, can result in injury to the user if the movement is not expected and a secure grip on the handle is not carefully maintained.
An additional problem with conventional systems arises from the additional handle movement required to move the connecting link to its overcenter position. With modern mowers, it is frequently difficult to accommodate the wasted handle movement in a package which seeks to maximize efficient body design.